The present invention relates to pressure-sensitive adhesive compositions; and more particularly to water vapor permeable pressure-sensitive adhesive compositions.
The present invention also relates to pressure-sensitive adhesive compositions suitable for medical and/or surgical bandage sheeting materials, including adhesive tapes.
The present invention more particularly relates to water vapor permeable, pressure-sensitive adhesives for medical and/or surgical bandage sheeting materials incorporating modified acrylate copolymers.
The present invention further relates to a pressure-sensitive adhesive which will cause minimum maceration or tissue damage of contacted skin areas, when used to attach a medical or surgical dressing or adhesive tape or bandage thereto.
The present invention still further relates to a water vapor permeable, pressure-sensitive adhesive composition which is at once both convenient to use and economical to manufacture.
The use of pressure-sensitive adhesive-coated sheet materials in the form of adhesive tapes, medical and surgical bandages, and surgical drapes for the management of skin wounds in order to protect the subject wounds from trauma, superficial dirt and bacterial contamination, also to absorb wound exudate, and to limit movement of tissues, is a widely practiced and well-accepted medical practice.
For many years, the pressure-sensitive adhesives that have been used for attachment of these dressing materials to the skin surface were natural rubber based, and therefore they contained the usual chemical additives, such as resins, plasticizers, anti-oxidants, etc. The foregoing listed chemical additives, in addition to others, are potentially irritating to human skin. In addition, as the pressure-sensitive adhesive and, in some cases, the dressing materials were occlusive and water vapor non-permeable by nature, the adhesive sheet materials led to water accummulation under them following their emplacement.
The accummulated water would then over-hydrate and soften the outer layers of the skin (stratum corneum), thus causing what is referred to as skin maceration. Further, the stratum corneum of the then macerated skin is readily further damaged when the pressure-sensitive adhesive-coated sheet material is removed. Therefore, in order to prevent the widely prevalent moisture-caused maceration of skin, the pressure-sensitive adhesive-coated sheet materials should preferably be composed of water vapor permeable adhesive substrate backings and non-irritating pressure-sensitive adhesives.
Many of the modern surgical adhesive dressings and bandages employ an acrylic-based pressure-sensitive adhesive, which is much more permeable to water than the prior art rubber-based occlusive adhesive compositions. Although acrylic-based pressure-sensitive adhesives are less traumatic to human skin than those which are rubber-based, they are not without their inherent disadvantages. Especially in applications where the pressure-sensitive adhesive-coated dressing sheet material is repeatedly applied to and then removed from the same area of the skin surface, e.g., as in the changing of a medical or surgical dressing, or when in place over a prolonged period of time, a significant local skin damage or water-induced maceration can result.
The present invention pressure-sensitive adhesive is a copolymeric composition, having improved pressure-sensitive adhesive properties and enhanced water vapor permeability. It is comprised of about 79 to 89 percent by weight of n-butyl acrylate, from about 10 to 20 percent by weight of a hydrophilic N-vinyl lactam, and from about 1 to 5 percent by weight of an acidic comonomer.
Pressure-sensitive adhesive compositions are commonly applied to the flexible backing or tape on which they are supported during use by coating them in the form of a solution or dispersion in a suitable vehicle such as an organic solvent or water, and evaporating the vehicle, or by coating them in the form of a hot melt free from vehicle. In order to be useful, pressure-sensitive adhesive compositions must possess not only good tack but also good cohesive strength and the desired high degree of adhesion. All of these properties are generally interdependent, a change in one usually causing a change in the others.
Conventional acrylic-based pressure-sensitive adhesive compositions are generally single component materials, comprised of copolymers of long chain alkyl acrylate (C.sub.4 -C.sub.8) esters with polar monomers such as acrylic acid, acrylonitrile, acrylamide, etc. Optional modifying monomers which may also be copolymerized with alkyl acrylate esters are methyl or ethyl acrylate, alkyl (C.sub.1 -C.sub.4) methacrylates, styrene, vinyl acetate, etc.
In order to achieve optimum cohesive and adhesive properties of the copolymer, a proper balance of its molecular weight (usually very high, from about 800,000 to more than about 1,000,000 mw), its polar character, and a glass transition temperature (T.sub.G) ranging from about -25.degree. C. to -70.degree. C., is necessary.
R. F. Peck (U.K. Pat. GB No. 2,070,631A) teaches the copolymerization of n-butyl acrylate, 2-ethylhexyl acrylate and acrylic acid to produce a polyacrylate having a K-value of from 90 to 110 claimed to result in a satisfactory water vapor permeability for use with medical dressings.
E. Schonfeld (U.S. Pat. No. 4,140,115) has proposed the incorporation of a polyol, such as polyoxyalkylene glycol, in the acrylic adhesive mass for use in surgical and/or medical bandages or tapes, which are claimed to result in less skin damage upon their removal.
Ono, et al, (U.S. Pat. No. 3,975,570) has proposed to improve the water vapor permeability of conventional acrylic pressure-sensitive adhesives by blending with them hydroxyethyl cellulose.
K. R. Shah (the present inventor) in his U.S. Pat. No. 4,337,325, has described blending alkyl acrylate-acrylic acid copolymers with certain proportions of N-vinyl lactam homopolymers and copolymers to obtain pressure sensitive adhesives having increased water vapor permeabilities.
H. Reinhard, et al, (U.S. Pat. No. 3,725,122) have disclosed a pressure sensitive adhesive comprising a copolymer of primary and/or secondary alkyl acrylate (C.sub.4 -C.sub.12) esters, of which at least 25 percent are derived from alkanols having 6 to 12 carbon atoms, tertiary alkyl (C.sub.4 -C.sub.12) esters, N-vinyl pyrrolidone (1 to 10 percent by weight), and olefinically unsaturated monomers (such as acrylic acid, acrylamide, etc.) containing reactive groups.
However, it should be noted that the presence of small amounts (i.e. 10 percent) of hydrophilic N-vinyl pyrrolidone, and the presence of hydrophobic long chain (C.sub.6 -C.sub.12) alkyl acrylate moities in the above-discussed copolymeric compositions, would not be expected to impart enhanced water vapor permeability to them.
In Martens, et al, (U.S. Pat. No. 4,181,752), a process for the free radical polymerization of acrylic monomers by means of ultraviolet irradiation under controlled conditions in order to prepare pressure sensitive adhesives is described and claimed. N-vinyl pyrrolidone and acrylic acid have been mentioned in Martens, et al, as monomers copolymerizable with alkyl acrylates by the irradiation process. However, copolymers of n-butyl acrylate, N-vinyl pyrrolidone, and acrylic acid as described and claimed in the present invention were not taught or considered by the above-discussed inventors.